A conventional trench gate metal oxide semiconductor field effect transistor comprises a gate structure, which is disposed within a trench. For fabricating the conventional trench gate metal oxide semiconductor field effect transistor, a trench is firstly formed in a semiconductor substrate, and then a gate dielectric layer is formed on a sidewall of the trench by thermal oxidation. Then, a polysilicon semiconductor material is filled into the trench. After a planarization process is performed, a polysilicon gate is formed in the trench.
Recently, since the integrated circuit becomes more complicated, the feature size and wiring space of the semiconductor device are gradually decreased, and the size of the polysilicon gate is reduced. After the polysilicon gate is formed, a metal contact plug is formed on the polysilicon gate in the subsequent process. As known, the size reduction of the polysilicon gate may result in misalignment between the polysilicon gate and the metal contact plug. If the metal contact plug is deviated because of misalignment, the metal contact plug and the neighboring circuits may be suffered from charge breakdown.
Therefore, there is a need of providing an improved trench gate metal oxide semiconductor field effect transistor and a fabricating method thereof in order to obviate the drawbacks encountered from the prior art.